Gitea tag delete route deletes releases without release permission

The Gitea web route for deleting tags (`POST /{owner}/{repo}/tags/delete`) requires only write access to the Code unit, but shares its handler with release deletion and did not check that the target was a plain tag. A collaborator with Code write access and without Releases write access could permanently delete published releases of that repository, including their attachments. Protected tag rules covering the release tag still blocked the deletion.